Seafood allergies can trigger a variety of allergic symptoms, most of which are very similar to those of other types of food allergies. These symptoms usually appear within two hours of eating, inhaling or touching seafood, but in some cases symptoms can be delayed up to 24 hours.

Reactions to a food allergen can range from mild anaphylaxis (generalized allergic reaction involving two or more body systems) to severe and potentially life-threatening anaphylactic shock. There is no way to predict the severity of reaction when a person with food allergies ingests the problem foods. Therefore, even people experiencing mild symptoms should immediately take a shot of epinephrine and seek medical treatment (see Treatment and prevention).

Mild to moderate symptoms of an allergic food reaction may include:

• Skin problems. Includes itchiness, hives or swelling.
  
  
• Gastrointestinal problems. Includes stomach cramps, diarrhea, nausea, heartburn and gas.
  
  
• Respiratory problems. Includes wheezing, coughing or difficulty breathing.
  
  
• Nasal or sinus problems. Includes runny nose, nasal congestion or sneezing. These symptoms (associated with allergic rhinitis) are more common when the fumes from seafood are inhaled during cooking, rather than when seafood is ingested.
  
  
• Oral problems. Includes tingling in the mouth or swelling of the tongue and throat.

Mild to moderate symptoms may progress rapidly to more severe symptoms. People having any kind of food reaction should seek immediate medical attention to prevent anaphylactic shock. It is also possible for severe symptoms to appear even when mild to moderate symptoms were not present. Symptoms of a more severe reaction include:

• Shortness of breath
• Tightening in the chest or throat
• Choking
• Loss of consciousness
• Drop in blood pressure